function convert(list) {
  const res = []
  const map = list.reduce((res, v) => (res[v.id] = v, res), {})
  for (const item of list) {
    if (item.parentId === 0) {
      res.push(item)
      continue
    }
    if (item.parentId in map) {
      const parent = map[item.parentId]
      parent.children = parent.children || []
      parent.children.push(item)
    }
  }
  return res
}

module.exports = convert
